An electromagnet has stored 540 J of magnetic energy when a current of 6 A exists in its coil. What is the value of average emf induced, if the current is reduced to zero in 0.54 s?

333.3 V

The correct answer is Option (1) → 333.3 V

To calculate the average emf induced $(ε_{avg})$ in the coil, we use faraday's law of electromagnetic induction -

$ε_{avg}=-L\frac{ΔI}{Δt}$

given,

Energy stored in a capacitor, U = 540 J

I, Current = 6A

and,

$U=\frac{1}{2}LI^2$ [formula]

$L=\frac{2U}{I^2}=\frac{2×540}{6^2}$

$L=30H$

$ΔI=I_{final}-I_{initial}=0-6=-6A$

$Δt=0.54s$ [given]

$ε_{avg}=30×\frac{6}{0.54}=333.3V$